Include drivers for all keyboards when MODULES=dep; include most USB host drivers and all bus driver modules; remove code that prunes 'broken' symlinks and sometimes /etc/mtab; add all I2C bus and mux drivers when MODULES=most; stop force-loading drivers found through sysfs when MODULES=dep

Fix build failure with Linux 4.x kernels; add delmap to .prerm for all packages that contain map data types exposed through external .so files so that upgrades to stretch (where the associated files have moved) will be functional